This is common behavior if the links are stored on a server and the various workstations are not time-synched properly.
Thanks for the reply. I checked the time and dates, and all the workstations and the server have the exact same values.
Could it have to do with the fact that the files are stored on a server with Windows Server 2008?
Other suggestions are also welcome
I've seen backup routines that change the archive bit cause this sort of error, too, I think.
I know this is a shameless plug but the place I work at has a subsidiary called Linktek. They have a product called LinkFixerPlus. It is Windows based and runs on InDesign all the way back to version 1.5. There is a 30 day free trial, so check it out and see if it is right for your situation.
I suppose there's a good reason your're still working in CS, but there are a l ot of improvements that will speed up your workflow if you upgrade, including the ability to bypass the missing/modified links when you open a file, if that's what you want to do, which was added in CS4.
Also keep in mind that using CS on a MacIntel CS has to run in Rosetta (PowerPC emulation mode) this adds a layer of weird problems that Adobe has no intention of fixing as the software is 3 versions old. On top of that CS is not supported in Leopard and will not be fix or updated for the reasons I mentioned in the last sentence.
You should update to CS4 before you lose your upgrade path when CS5 is released.
That backup procedure had no impact on the files. Files that were fine before, were fine after ther backup.
Thanks for the other comments.
I wasn't trying to say that the files were in any way damaged or the data changed by the backup, just that I'd seen InDesign treat links as modified when the only thing done to them was they were accessed for backup.